Modeling and Numerical Simulation of Material Science, 2013, 3, 23-27
Published Online January 2013 (http://www.SciRP.org/journal/mnsms)
Synthesis of Barium Nickel Titanium Oxide Stabilized by
Citric Acid
K. Y. Chew, M. Abu Bakar*, N.H.H. Abu Bakar
Nanoscience Research Laboratory, School of Chemical Sciences, Universiti Sains Malaysia, 11800 USM Pulau Pinang, Malaysia.
Received 2012
ABSTRACT
Barium nickel titanium oxide particles (Ba2NiTi5O13) were synthesized in the presence of citric acid by using a two step
sol-gel method followed by calcination. The addition of citric acid as a stabilizer (mole ratio of 0.5, 1.0, 2.0, 4.0) re-
sulted in the formation of Ba2NiTi5O13 particles with various morphology (i.e. sphere, cube, rod). These various mor-
phology changes were deduced to be caused by citric acid that tends to absorbed on certain dimension of the
Ba2NiTi5O13 particles when different concentration of citric acid was added. Besides that, the growth of Ba2NiTi5O13
particles from incorporation of bulky micelles which act as a protective 'shell' that control particle sizes by attaching on
the surfaces of particles.
Keywords: Barium Nickel Titanium Oxide; Citric Acid; Morphology
1. Introduction
Ceramic perovskite materials have gained a lot of interest
because they are exploited as industrial electrodes [1],
catalysts [2, 3], electronic components [4] and so on. The
high demand for these materials is ascribed to their
unique characteristics such as high mechanical strength,
high temperature stability and lowered sintering
temperature of ceramic materials as well as high surface
area. Recently, perovskite structured metal oxides (AB O 3)
has become a promising heterogenous catalyst as it
provides features suitable for green sustainable
techno lo g y [2,3] and also has high porosity which re-
sulted in a better catalyst life [3]. The structure of
perovskite ceramics (ABO3) is where A is the larger
cations from alkaline metal groups whereas B is the
smaller cations from transition metal groups. Either site
of A/B or both cations are responsible for the respective
catalytic reaction. Therefore, this material can reduce the
usage amount of the commonly expensive noble metals
such as Pd, Pt and Rh [3]. Certain binary, ternary and
quaternary metal oxides that contain 2, 3 and 4 different
metal elements also belong to the perovskite-type mixed
oxides materials. Barium nickel titanium oxide
(Ba2NiTi5O13) is an example of quaternary perovskite
structured material [5].
Conventional solid state milling methods require high
calcination temperatures and pressure, which can cause
agglomeration of particles which in turn can cause the
coarsening the surface of particles. This is undesirable as
it can affect the chemical and physical properties of the
particles [6,7].
Therefore, many wet chemical synthesis methods have
been introduced to compensate these problems such as
hydrothermal [8], coprecipitation [9] molten salt route
[10] and sol gel [11]. The sol gel method is a common
wet chemical method because it exhibits several advan-
tages such as low processing cost, excellent chemical
homogeneity, low processing temperature as well as
good stoichiometrically control of the elements of the
synthesized compound. However, refined shaped and
non agglomerated particles are commonly achieved by
addition of supports which are then difficult to be re-
moved. These supports such as polymers and surfactants
have often been used in these supports assisted sol gel
synthesis are able to control particles sizes and modify
particles morphology [12]. However, total removal of
carbonaceous substances by calcinations after the incor-
poration of these supports is difficult [12].
Citric acid stabilized sol gel method, which is
commonly known as the Pechini method, are practiced
by using citrate salts or mixtures of co mmo n salts with
citric acids as precursor. This citrate will form
complexations via its carboxylate groups with empty
orbitals of metals [13]. Because of this, citric acid is well
known as a stabilizer in nanoparticles synthesis by
functioning as ligand, or act ing as a particle surface
modifier [4,7,14]. Therefore, the objective of this study is
*Corresponding author.

K. Y. CHEW ET AL.
to investigate the effect of citric acid on the morphology
of barium nickel titanium oxide particles prepared via a
two steps of sol gel method.
2. Methodology and Materials
2.1. Experimental
Similar procedures for preparing barium nickel titanium
oxid e via the two steps sol gel method as discussed pre-
viously [15] was employed. However, in this experiment,
citric acid (C6H8O7, 99.5%, Merck) was added in both
steps after adding nickel acetate tetrahydrate and barium
hydroxide monohydrate respectively. Half the amount of
citric acid was added during the first step, and the other
half amount of citric acid is added in the second step.
Detail mole ratio of each reactant with designated sample
numbering is tabulated in Table 1.
Table 1. Details mole ratio of reactants used.
Mole Ratio of Reactan ts
Desi gn a-
tion
Ba(OH)2.H2
O
Ni Ac2.4H2
O Ti(O Pr i)4 Citric Acid
Sample 1 1 .2 1 .2 1 0.5
Sample 2 1 .2 1 .2 1 1.0
Sample 3 1 .2 1 .2 1 2.0
Sample 4 1 .2 1 .2 1 4.0
2.2. Characterization
X-Ray Diffraction (XRD) analysis was performed using
a SIEMENS D5000 X-Ray Diffractometer with a
monochromatic Cu-Kα radiation filter in the 2θ range of
20-90 °. Fourier Transform Infrared (FTIR) spectra were
obtained by scanning from 4000-400 cm-1 and the
resolution employed was 4 cm-1 using a Perkin-Elmer
System 2000 infrared spectrometer. The sample were
coated with a thin layer of gold on the surface to prevent
discharge and average size of synthesized Ba2NiTi5O13
was determined by Scanning Electron Microscopy (SEM)
performed using a Leica Cambridge Stereoscan S360
operated at 15 kV.
3. Results and Discussion
3.1. Structural Composition (XRD)
The phase composition was investigated by using XRD,
which is shown in Figure 1. All major peaks are attri-
buted to barium nickel titanium oxide, and these peaks
matc h with the JCPDS card number 01-086-0207. Some
minor impurities attributed to the organic peaks of re-
maining citric acid are also observed. The phase of
Ba2NiTi5O13 is monoclinic and there are 12 major peaks
which are indicated at 2θ angles of 24.415º, 29.014º,
29.806º, 30.358º, 31.562º, 33.724º, 37.486º, 38.928º,
43.715º, 43.980º, 44.071º and 46.385º that are corres-
ponding to <-401>, <310>, <-311>, <-203>, <112>,
<311>, <-312>, <-113>, <601>, <-404>, <313>, <602>
and <020> respectively.
Figure 1. Typical XRD diffractogram of barium nickel tita-
nium oxide stabilized by citric acid.
3.2. Molecular Structure (FTIR)
The effect of citric acid incorporation on the surface of
barium nickel titanium oxide wa s investigated via FTIR
and is shown in Figure 2. The FTIR spectra of citric acid
(Figure 2(a)) is compared to the barium nickel titanium
oxide incorporated with various amount of citric acid
(Figure 2(b)-(e)). The spectra of citric acid demonstrate a
broad band at ~3590 cm-1 corresponding to the stretching
vibration of OH group from citric acid. Sharp splitting
bands at wavenumbers of 2360 and 2334 cm-1 due to the
vibration bands from C-H stretching mode of citric acid
are also observed [16]. Besides, stretching bands at wa-
venumbers of 1810 and 1513 cm-1 which correspond to
asymmetric and symmetric stretching vibrations of car-
boxylate (COO-) from bidendate ligand citric acid re-
spectively are also available [16]. Other smaller vibration
bands observed are also the stretching bands of the or-
ganic substances.
FTIR spectrum of neat Ba2NiTi5O13 has been reported
in [15]. Upon incorporation of Ba2NiTi5O13 with citric
acid as shown in Figure 2(b)-(e), the broad vibration
bands to wavenumbers of 3433-3470 cm-1 occurs. This is
due to the possibility of absorption of moisture from KBr
pellet. Besides, some vibration bands corresponding to
citric acid are not observed. However, those asymmetric
and symmetric stretching vibration representing vibration
bands of carboxylate (COO-) from carbonate are corres-
ponding to 1670 cm-1 and 1432 cm-1 wavenumbers
respectively as observed in Figure 2(b)-(e). These carbo-
Lin (Counts)
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
2-Theta - Scale
20 30 40 50 60 70 80 90
24

K. Y. CHEW ET AL.
nate bands formed from calcination of citric acid with
addition of Ba2NiTi5O13. This may indicate that
incorporation of citric acid on Ba2NiTi5O13 particles by
forming complexation has occurred previously before
calcination [16]. In addition, 857 cm-1 wavenumber are
corresponded to asymme tric stretching of carbonate [15].
Formation of carbonate in Ba2NiTi5O13 even after calci-
nations may be due to incomplete calcinations of organic
substances in those samples. On the other hand, a broad
absorption at wavenumber ~540 cm-1 represents charac-
teristic stretching vibration of Ti-O from perovskite
phase structure formation as in Ba2NiTi5O13 [17] can also
be observed. Therefore, incorporation of citric acid on
Ba2NiTi5O13 has occurred.
Figure 2. FTIR spectra of (a) citric acid; (b) Sample 1; (c)
Sample 2 (d) Sample 3 and (e) Sample 4 after calcination at
900 °C for 8 hours.
3.3. Morphology of Ba2NiTi 5O13 (SE M)
The morphology of citric acid stabilized Ba2NiT i 5O13 is
not homogeneously spherical as observed for the neat
Ba2NiTi5O13 [15]. In Sample 1 which is shown in Figure
3, when the mole ratio of citric acid used is 0.5, cubic
shape d of Ba2NiTi5O13 particles were formed. An
inhomogeneous size of particles existed (average size =
0.78 ± 0.56 μm). By continuously increasing the mole
ratio of citric acid to 1.0 (Sample 2) as shown in Figure 4,
the particles fo rmed is still cubic shaped ho wever with
better size distribution (0.35 ± 0 .13 μ m). When the mole
ratio of citric acid is 2.0 (Sample 3) as shown in Figure 5,
some smal l cubic shaped particles still exist (average size
= 0.31 ± 0.18 μm) however most of the particles are in
the form of rods with an average length 7.01 ± 3.19 μm.
By adding citric acid up to a mole ratio of 4.0 (Sample 4)
which is shown in Figure 6, neither cube shape nor rod
shape particles can be seen. Instead spherical shaped
particles with an average size of 0.60 ± 0.39 μm particles
are observed.
The particles size transformation of barium nickel tita-
nium oxide with increasing amount of citric acid as sta-
bilizer can be explained according to the ‘protective
shell ’ concept. When the amount of citric acid increases,
the precursor nuclei are repulsed by the increasing
amount of steric hindrance from the long carbon chain of
citric acid. Thus, the precursor nuclei are forced apart
before they have the chance to collide with each other
and form bigger precursor nuclei. Therefore, the larger
the amount of citric acid, the smaller the particles formed.
Nevertheless, the spherical particle sizes are larger than
the non-citric acid incorporated on Ba2NiTi5O13 particles
reported in [15]. In this case, citric acid may be facilitat-
ing formation of bigger micelles and thus bigger particles
as compared to non-citric acid incorporated Ba2NiT i 5O13
particles as the formation of them do not need to be re-
stricted by the micelles.
Citric acid is believed to act as a surfactant. When
dissolved in water, surfactant attracts with each other to
form micelles. These micelles are the core center of
particles formation. As observed, the morphology
transformation of barium nickel titanium oxide occurred
with different amounts of citric acid. Lower amounts of
citric acid addition helped the surfactant to form rod
shaped particles. Nevertheless, when the amount of citric
acid increases high enough as in Sample 4, citric acid
tends to form spherical micelles that facilitate the
formation of spherical particles. Citric acid may be tends
to absorbed on certain dimension of Ba2NiTi5O13 par-
ticles when different amount of citric acid is added.
When the mole ratio of citric acid is 0.5%, citric acid is
absorbed on both horizontal and vertical axial forming
cubic shaped Ba2NiTi5O13 particles. As increasing the
citric acid concentration, the increased amount of citric
acid tends to absorbed more on horizontal dimension and
thus forming rod shaped Ba2NiTi5O13 particles. However,
when the mole ratio of citric acid increases to 4.0%, the
excess of citric acid are absorbed on every dimension of
Ba2NiTi5O13 particles and thus forming many smaller and
spherical shaped particles. Figure 7 shows the tentative
schematic diagram of these morphology changes of
Ba2NiTi5O13 particles. Therefore, citric acid is not only
able to control the size of Ba2NiTi5O13 particles, but also
able to control the morphology of particles.
4. Conclusion
Complexation of citric acid incorporation on
Ba2NiTi5O13 was found to occur. Formation of a
protecting shell of citric acid was deemed to be able to
stabilize as well as modify the morphology of core
barium nickel titanium oxide particles. Rod shaped or
cubic shaped particles formed when small amount of
citric acid was used. However, when the citric acid con-
tent wa s increased to 4.0 mole %, more homogenous and
nearly spherical particles with an average size of 0.60 ±
0.39 μm wer e observed.
25

K. Y. CHEW ET AL.
5. Acknow l edge ments
This work is financially supported by the USM Research
University Postgraduate Research Grant Scheme
(RUPGRS). Great appreciation is given to USM
Fellowship and to lab technicians for helping in
operating instruments and equipments.
Figure 3. SEM micrograph of Sample 1 magnified 20000
times.
Figure 4. SEM micrograph of Sample 2 magnified 20000
times.
Figure 5. SEM micrograph of Sample 3 magnified 20000
times.
Figure 6. SEM micrograph of Sample 4 magnified 20000
times.
Figure 7. Tentative schematic diagram for morphology
changes of Ba2NiTi5O13 particle s .
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